Melting behaviour of a series of diamides

The melting behaviour of diamides of general formula (n — C_pH_2p+1)CONH-(CH₂)_qNHCO(n — C_pH_2p+1) has been investigated by calorimetric, dilatometric and IR techniques. The conformational contribution to the melting entropy, calculated from the hypothesis of complete conformational freedom of the molecules at the melting point, has been compared with the experimental data. The higher melting points of the diamides, as compared with those of the linear hydrocarbons having the same number of conformationally flexible chain bonds, are attributed to a reduction of conformational freedom of the chain segments in the liquid state (caused by the large fraction of hydrogen bonds maintained in the melt).     

Conformational freedom of polyamide chains above the melting point

The melting behavior of diamides of general formula (n-C_pH_2p+1)CONH(CH₂)_qNHCO(nC_pH_2p+1) has been investigated by differential scanning calorimetry (DSC). The close similarity of the melting behavior of these low molar mass compounds with that of polymeric amides is discussed in terms of restricted conformational disorder in the amorphous state, due to the high degree of retention of hydrogen bonding.     

Intramolecular easily polarizable hydrogen bonds with anilides of 1-piperidine carboxylic acids

IR spectra are plotted from anilides of 1-piperidine carboxylic acids C₅H₁₀N(CH₂)_n CONHC₆H₄R in CHCl₃ and CDCl₃ solutions. In the cases of n = 1 and n = 4, weak intramolecular (NH?N) hydrogen bonds are formed. An asymmetrical energy surface occurs and the proton is present at the N of the anilide group. In the cases of n = 2 and n = 3, intramolecular proton transfer hydrogen bonds of the types N_BH?N_P ? ^?N_B?H⁺N_p are formed. In contrast to the intramolecular OH? N ? O^?1 ? H⁺N bonds with 1-piperidine carboxylic acids, these bonds to not cause IR continua but two bands: one in the region 3250–3190 and one in the region 2500–2450 cm^?1. The fact that, instead of IR continua, bands are observed is explained by the following: (1) these hydrogen bonds are relatively long; (2) they show only a narrow distribution of bond length; (3) the electrical fields at these bonds are small, since they are strongly screened.     

Thermal behaviour of mixed long-chain alkylammonium tetrachlorozincates

Mixed crystals of composition (n-C_mH_2m+1NH₃)_2xm(n-C_nH_2n+1 · NH₃)_2?2xm ZnCl₄ (m= 12; n=14, 16, 18) are formed upon annealing mechanical mixtures of layer compounds (n-C_nH_2n+1NH₃)₂ZnCl₄, through solid state diffusion of the n-alkylammonium cations. From a common high temperature monophasic modification, in which the polymethylenic chains are conformationally molten, different modifications are obtained on cooling [depending on the (n ? m) value] in which chain crystallinity is developed. The structure of such modifications is speculated on the grounds of DSC and preliminary X-ray diffractometric and IR data, and compared with that of similar previously characterized systems.     

New neutral and cationic cyclopentadienylcobalt complexes

The treatment of the aquocation [Co(η³-2-MeC₃H₄)(η⁵-C₅H₅)(H₂O]⁺ with neutral and anionic ligands gives new cobalt complexes containing cations [Co(η³-2-MeC₃H₄)(η⁵-C₅H₅)L]ⁿ⁺, n = 0; L = CN, CH₃COO, CF₃COO and n = 1; L = P(p-MePh)₃, NCEt, NCPh, CNCy, dppm and [{Co(η³-2-MeC₃H₄)(η⁵-C₅H₅)}₂ (μ-L-L)]²⁺, L-L = bipy, dppm. The neutral cyano complex reacts with various electrophiles to give cationic isocyanide complexes containing the cation [Co(η³-2-MeC₃H₄)(η⁵-C₅H₅)(CNR)]⁺, which have been isolated in low yields. Chemical behaviour and structural implications of IR and ¹H and ¹³C NMR spectra are discussed.     

Thermodynamic Properties of the n-Alkanes C19H40 to C26H54 and Their Binary Phase Diagrams

The shapes of the C₂₂H₄₆-C₂₄H₅₀ and C₂₃H₄₈-C₂₄H₅₀ binary phase diagrams were analyzed. In the C₂₂H₄₆-C₂₄H₅₀ binary system the increased stability of the binary compounds with increasing temperature can be explained by the much larger heat capacity and entropy of the binary compounds compared to that of the components C₂₂H₄₆ and C₂₄H₅₀. In the C₂₃H₄₈-C₂₄H₅₀ system this effect is much less pronounced. The measured enthalpy data of n-alkanes C₁₉H₄₀ to C₂₄H₅₀ and of the binary system C₂₂H₄₆-C₂₄H₅₀ were analyzed to obtain the ‘excess’ heat capacity per atom of carbon {[C _p/(Rm)]-3} (Rm being the number of carbon atoms). The ‘excess’ heat capacity per carbon atom is the value of the heat capacity above the Debye high temperature value of 3R. At low temperatures (below 280 K) one is in the Debye temperature θ_D region. At higher temperatures the large ‘excess’ heat capacity of the solids explains the movements in the carbon chains. In the liquid the excess heat capacity is small and corresponds numerically to the anharmonic vibrations in low melting metals. In contrast to metals, where the difference in heat capacity between liquid and solid below the melting point is positive C _p(L-s)>0, in the alkanes studied it is strongly negative C _p(L-s)?0. This explains the shape of the binary phase diagrams C₂₂H₄₆-C₂₄H₅₀, C₂₄H₅₀-C₂₆H₅₄, C₂₂H₄₆-C₂₃H₄₈ and C₂₃H₄₈-C₂₄H₅₀.     

Two inclusion compounds of guanylthiourea and 1,3,5-thiadiazole-5-amido-2-carbamate

In the crystal structure of [(n-C₄H₉)₄N]⁺·[NH₂(C₂N₂S)NHCOO^?]·NH₂CSNC(NH₂)₂ (1), guanylthiourea molecules and 1,3,5-thiadiazole-5-amido-2-carbamate ions are joined together by intermolecular N–H…O, N–H…N, and weak N–H…S hydrogen bonds to generate stacked host layers corresponding to the (110) family of planes, between which the tetra-n-butylammonium guest cations are orderly arranged in a sandwich-like manner. In the crystal structure of [(n-C₃H₇)₄N]⁺·[NH₂(C₂N₂S)NHCOO^?]·NH₂CSNC(NH₂)₂·H₂O (2), the tetrapropyl ammonium cations are stacked within channels each composed of hydrogen bonded ribbons of guanylthiourea molecules, 1,3,5-thiadiazole-5-amido-2-carbamate ions and water molecules.     

Combined Fourier transform infrared and Raman spectroscopic studies of some carbonyl-diphosphine-indenyl-iron cations

The Fourier transform infrared and Raman spectra of the cations [η⁵-C₉H₇Fe(CO)_n dppa]⁺ (n = 1, 2; dppa=bisdiphenylphosphinoalkane, where alkane=methane, ethane, butane, hexane and octane) and [{η⁵-C₉H₇Fe(CO)₂}₂-μ-dppa]²⁺ indicate that the alkyl chain lengths have effects on the structures of the bidentate cations resulting in increased back-donation to carbonyl groups as the chain length increases. In contrast the alkyl chain lengths have no similar effects in the unidentate mononuclear and bridged cations.     

The confirmation of the formation of clathrate-like hydrates of poly(tetrabutylammonium ethenesulfonate) and of poly(tetraisopentylammonium ethenesulfonate)

A thermal method using differential scanning calorimeter has been applied to aqueous solutions of a series of poly(tetraalkylammonium ethenesulfonates) (R₄NPES). It was found that only the salts withR=n-C₄H₉ andR=i-C₅H₁₁ could form stable hydrates having large hydration numbers. The melting point and hydration numbers of these two hydrates were 12.0°C and 30±1 for the (n-C₄H₉)₄NPES hydrate and 16.0°C and 53±2 for the (i-C₅H₁₁)₄NPES hydrate, respectively. It was concluded that these hydrates were clathrate-like essentially similar to such hydrates as (n-C₄H₉)₄NF·30H₂O and (i-C₅H₁₁)₄NF·40H₂O.     

Synthesis,characterization and computational study of 1D-MOFs of Co (II)

Two new metal–organic frameworks {[Co(pBrBz)(H₂O)₂](pBrBz)(H₂O)} _n (1) and {[Co(pBrBz)₂(pBrBzH)(4,4′-bpy)]} _n (2) (4,4′-bpy=4,4′-bipyridine; pBrBzH=p-bromobenzoic acid) have been synthesized by solvothermal method and characterized by single-crystal X-ray diffraction and thermogravimetric analysis. The structure of (1) reveals an infinite linear 1D chain with a Co^···Co short separation in which each pBrBz ligand bridges two adjacent Co(II) ions. Compound (2) is a neutral linear polymer of cobalt; every two adjacent chain are orderly packed via intermolecular interactions, combined stacking interactions, weak hydrogen and halogen bonds are responsible of 3D supramolecular architecture. The thermal decomposition of both complexes has been investigated and shows a long-range temperature stability. DFT calculations carried out on ligands are schematically illustrating the nature of solid-state architecture of (2).     

The mass spectra of alkyl phenyl tellurides

The mass spectra of several alkyl phenyl tellurides, C₆H₅TeR (R = CH₃, CD₃, C₂H₅, n-C₃H₇, i-C₃H₇ and n-C₄H₉) have been studied with special emphasis on the fragmentation patterns involving cleavage of the alkyl and aryl tellurium–carbon bonds. Each compound exhibited intense parent ions. The rearrangement ions [C₆H₆Te]⁺? and [C₆H₆]⁺? were found in the spectra of phenyl ethyl and higher tellurides. Two other rearrangement ions [HTe]⁺ and [C₇H₇]⁺ were observed in the spectrum of each compound. Examination of the mass spectrum of phenyl methyl-d₃ telluride demonstrated that the [HTe]⁺ ions derive hydrogen from the phenyl group.     

Photolysis of poly(p-isopropyl styrene)

The photodegradation of films of poly(p-isopropyl styrene) with 254 nm radiation at 10^?6mbar and 25±1° has been studied. The principal product is hydrogen but smaller quantities of methane and ethane and a trace of propane are also formed, indicating that the p-substituent also undergoes decomposition. Ultraviolet spectra show rapid changes, particularly in the 230–240 nm region, and a long wave absorption system extending into the visible region also appears. Solubility data indicate the simultaneous occurrence of cross-linking and chain scission, rates of both processes being significantly greater than those for poly(styrene); these results are explicable in terms of the inductive (+I) stabilization (due to the p-C₃H₇ group) of radicals formed on chain scission and of the participation of the p-C₃H₇ group in addition reactions. Quantum yields for the evolution of the gaseous products have been estimated.     

Thermal behavior of complexes of general formula (n-CnH2n+1NH2)2CuCl2

The thermal behaviour and some relationships between the physical properties and structure of complexes of general formula (n-C_nH_2n+1NH₂)₂CuCl₂, with n = 10, 12, ? 18, have been investigated by DSC and X-ray powder diffraction techniques. The high enthalpy solid—solid phase transitions observed for the complexes in the temperature range 350–390 K could be associated with the disordering of the hydrocarbon regions of the structure, as already observed for other similar layer compounds.     

The hapticity of octafluorocyclooctatetraene in its first-row mononuclear transition metal carbonyl complexes: effect of perfluorination

The iron tricarbonyl complex of octafluorocyclooctatetraene was synthesized by Hughes and co-workers and shown by X-ray crystallography to have a trihapto–monohapto structure (η^3,1-C₈F₈)Fe(CO)₃ in contrast to the tetrahapto structure (η⁴-C₈H₈)Fe(CO)₃ formed by the non-fluorinated cyclooctatetraene. This difference has stimulated a comprehensive density functional theoretical study of the octafluorocyclooctatetraene metal carbonyl complexes (C₈F₈)M(CO) _n (n = 4, 3, 2, 1 for M = Ti, V, Cr, Mn, and Fe; n = 3, 2, 1 for M = Co, Ni) for comparison with their hydrogen analogues (C₈H₈)M(CO) _n . In most such systems, the substitution of fluorine for hydrogen leads to relatively small changes in the preferred structures. However, for the iron carbonyl derivatives (C₈X₈)Fe(CO)₃ (X = H, F), the difference observed experimentally has been confirmed by theory with (η^3,1-C₈F₈)Fe(CO)₃ and (η⁴-C₈H₈)Fe(CO)₃ being the lowest energy structures by 4 and 14 kcal/mol, respectively. The ligand exchange reactions C₈H₈ + (C₈F₈)M(CO) _n  → C₈F₈ + (C₈H₈)M(CO) _n are predicted to be exothermic for almost all of the systems considered, with the (η^3,1-C₈X₈)Fe(CO)₃ system being the main exception. This suggests that the C₈F₈ ligand generally bonds more weakly to transition metals than the C₈H₈ ligand in accord with the electron-withdrawing effect of the ligand fluorine atoms.     

Crystal structure of mixed-ligand silver(I) hydrogen iminodiacetate

The crystal structure of mixed-ligand silver(I) hydrogen iminodiacetate has been studied. The composition of the [Ag₂(C₄H₆NO₄)(NO₃)(H₂O)] _n ([Ag₂(HIda)(NO₃)(H₂O)] _n ) coordination polymer has been refined. The NO₃ and H₂O ligands in the complex form rather weak coordination bonds with the Ag atoms. The system of hydrogen bonds in the structure has been considered. The formation of a chain of hydrogen bonds between the disordered H₂O molecules was established.     

Water-soluble (η-arene)ruthenium(II)-phosphine complexes and their catalytic activity in the hydrogenation of bicarbonate in aqueous solution

The reactions of [(η⁶-C₆H₆)RuCl₂]₂ and [(η⁶-p-cymene)RuCl₂]₂ with hydrogen in the presence of the water-soluble phosphines tppts (meta-trisulfonated triphenylphosphine) and pta (1,3,5-triaza-7-phosphaadamantane) afforded as the main species [(η⁶-C₆H₆)RuH(tppts)₂]⁺, [(η⁶-C₆H₆)RuH(pta)₂]⁺, [(η⁶-p-cymene)RuH(tppts)₂]⁺ and [(η⁶-p-cymene)RuH(pta)₂]⁺. This latter complex was also formed in the reaction of [(η⁶-p-cymene)RuCl₂(pta)] and hydrogen with a redistribution of pta. In addition, prolonged hydrogenation at elevated temperatures and in the presence of excess of pta led to the formation of the arene-free [RuH(pta)₄Cl], [RuH(pta)₄(H₂O)]⁺, [RuH₂(pta)₄] and [RuH(pta)₅]⁺ complexes. Ru-hydrides, such as [(η⁶-arene)RuH(L)₂]⁺, catalyzed the hydrogenation of bicarbonate to formate in aqueous solutions at p(H₂)=100 bar, T=50-70 °C.     

A thermogravimetric study of lithium tetraalkoxyborates

Properties of lithium tetraalkoxyborates Li[t-C₄H₉OB(OR)₃] (R = n-C₄H₉ to n-C₈H₁₇, n-C₁₂H₂₅) were studied by differential thermogravimetry. The kinetic parameters and heat effects of thermal decomposition of lithium tetraalkoxyborates in air and inert gas atmosphere as functions of the carbon chain length were determined.     

Synthesis, Structure and Thermal Property of [(n-C16H33)N(CH3)3]2[TiF6]·2H2O

A new compound dicetyltrimethylammonium hexafluorotitanium dihydrate, [(n-C₁₆H₃₃)N(CH₃)₃]₂[TiF₆]·2H₂O (compound 1), was hydrothermally synthesized at 150 °C and characterized by single crystal X-ray diffraction, Fourier-transform infrared (FTIR) spectroscopy, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in the monoclinic system, space group C2/c. It consists of hexafluorotitanium cations [TiF₆]²⁻, water molecular (H₂O), and cetyltrimethylammonium ions [(n-C₁₆H₃₃)N(CH₃)₃]⁺, which are connected together by extensive hydrogen bonding.     

Anionic alkyl diglycoldiamides with covalently bonded cobalt bis(dicarbollide)(1−) ions for lanthanide and actinide extractions

Ionic diamides composed of a N,N′-dialkyl diglycolyl complexing group and two cobalt bis(dicarbollide)(1−) anions were synthesized with the aim to develop efficient extraction agents for liquid-liquid extraction of polyvalent cations, i.e. lanthanides and actinides from high-level activity nuclear waste. Compounds of general formulation [{(N,N-(8-CH₂-CH₂O)₂-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co)(N′,N′-R)NCOCH₂}₂O]Na₂, where R = n-C₄H₉, n-C₈H₁₇, n-C₁₂H₂₅ and 1-C₆H₄-4-CH₃ (1-4), were prepared and characterized by combination of ¹¹B ¹H, ¹³C NMR spectroscopy, ESI-MS, HPLC and other techniques. Effects of different nitrogen substitution in the structures of 1-4 on the extraction properties were tested. The study resulted in the observation that the compounds are significantly (2-3 orders in magnitude) more efficient extractants for Eu(III) and Am(III) than synergic mixtures of organic N,N′-tetra n-octyl diglycolic acid diamide (TODGA) and chlorinated cobalt bis(dicarbollide) at the same concentrations of both groups. Low polar mixtures of n-dodecane (D) and hexyl methyl ketone (HMK) can be applied as an auxiliary solvent for extraction, replacing thus the polar and less environmentally friendly nitro-, fluoro- and chloro- solvents used in the current dicarbollide liquid-liquid extraction process.     

Low frequency Raman spectra and librational lattice mode of triclinic n-paraffins

Polarized Raman spectra of a single-crystal specimen of triclinic n-C₂₄H₅₀ were measured. A weak band at 63 cm⁻¹ (at room temperature) was found to exhibit (ab′) polarization and to become very sharp and distinguishable at liquid helium temperature. A similar weak band was found in other members of triclinic n-paraffins at almost the same frequency independently of chain length. This characteristic band series was thought to be due to the librational lattice mode about the chain axis. The observed polarizations of the Raman bands corresponding to the transverse acoustic modes of the triclinic (or monoclinic) polyethylene lattice suggested an appreciable mixing between the in-plane and out-of-plane vibrations. The observed frequencies of n-C₂₄H₅₀ were compared with those obtained from the calculated dispersion curves of the monoclinic polyethylene lattice.